At the present time, due to an increase in broadband services, the number of FTTH subscribers using an optical fiber rapidly increases. As a result, in maintenance of infrastructure such as a conduit line that lays an optical fiber cable, a space to additionally lay the optical fiber cable is insufficient. For this reason, if the optical fiber cable is constructed to have the minute diameter and the high density, this becomes very effective in making effective use of infrastructure equipment.
As the optical fiber cable that is constructed to have the small diameter and the high density, for example, Patent Document 1 suggests a multiple optical fiber cable that has the very small diameter and the high density using a structure in which sheathing is applied on the outer circumference of a bundle where optical fibers with low optical loss increase with respect to bending and mono-coated optical fibers coated at the outer circumference of the above optical fibers are collected. However, since the optical fiber cable described in Patent Document 1 uses the mono-coated optical fiber, when an optical fiber transmission path is constructed, optical fiber cables need to be connected to each other. Therefore the optical fiber cable described in Patent Document 1 has a problem that the number of times of connecting the optical fibers increases, which results in deteriorating connection efficiency.
Meanwhile, an optical fiber ribbon where the plural mono-coated optical fibers arranged in parallel are collectively coated is an optical fiber unit where collective connection is enabled by a mass-splicing machine, and is widely used in the conventional optical fiber cable. However, the conventional optical fiber ribbon has bending anisotropy in which it is difficult to bend the optical fiber ribbon in a width direction from the shape thereof. If the conventional optical fiber ribbon receives bending in the width direction in the optical fiber cable, large distortion or optical loss is generated in the optical fiber. For this reason, it is needed to use an optical fiber ribbon or cable structure that can suppress the distortion or optical loss.
Accordingly, optical fiber cables using an optical fiber ribbon having a new structure are suggested.
In all optical fiber cables that are described in Patent Documents 2 to 5, an optical fiber ribbon where plural mono-coated optical fibers are intermittently bonded in a longitudinal direction is used, and single fiber separating performance of separating only a desired optical fiber from the optical fiber ribbon at the time of intermediate post branching of the optical fiber cable is mainly improved.
The optical fiber cables that are described in Patent Documents 2 and 3 are stored in the cables in a staked state, using the optical fiber ribbon where resin portions bonding all parts of plural mono-coated optical fibers arranged in parallel in a width direction are intermittently disposed in a longitudinal direction.
The optical fiber cable that is described in Patent Document 4 is stored in the cable in a stacked state, using an optical fiber ribbon where the optical fiber cable is intermittently segmented in the course of manufacturing the conventional optical fiber ribbon and the segmented portions are deviated in the width direction along the longitudinal direction of the optical fiber ribbon. Also, it is described that if the segmented portions are disposed in a twist inversion portion of an optical fiber cable with an SZ-slotted rod, warping of the optical fiber can be reduced, with respect to bending of the width direction received when the optical fiber ribbon is manufactured.
The optical fiber cable uses an optical fiber ribbon in which the resin portions bond two adjacent single-core coated optical fibers of the mono-coated optical fiber, the length of the resin portions is shorter than the length of non-bonded portions, and the resin portions adjacent in the width direction are disposed away from each other, and is folded in the cables and stored. Since the optical fiber ribbon has small bending anisotropy and is easily folded in a cylindrical shape, an optical fiber cable that has the small diameter and the high density can be manufactured, similar to the bundle of mono-coated optical fibers.